The ultrasound probe expands and contracts e.g., at 20kHz, thereby transmitting respectively 20,000 vibrations per second into the medium. High-power ultrasound is considered ultrasound in the range of 16-30kHz. In order to create acoustic cavitation, high-intensity, low-frequency ultrasound is generated by an ultrasound transducer and transmitted via ultrasonic horn and probe (sonotrode) into a liquid. The ultrasonic production of emulsions and nano-emulsions (such as oil-in water and water-in-oil emulsions) is based on the working principle of acoustic cavitation. The Working Principle of Ultrasonic Emulsification A few seconds of sonication turn the separate water/oil phases into a fine emulsion. Ultrasonic preparation of an oil-in-water (O/W) emulsion (red water / yellow oil). The droplet size of ultrasonically produced emulsions is a function of processing time and ultrasonic amplitude for both batch and continuous processing. However, nano-emulsions with uniform droplet size of 10nm can be easily and reliably achieved under optimized conditions. (2015) show in their study that ultrasonic emulsification consistently yielded submicron emulsions (less than 200 nm). Ultrasonic technique give more stable emulsions than the conventional mechanical agitation method. When compared to mechanial agitation, emulsions prepared by ultrasonic technique were found to be more stable for longer duration of time when compared to emulsions prepared by mechanical agitation which can be attributed to the small droplet size which is thermodynamically stabilized. Aggregation in the coconut oil-in-water emulsions appeared only after being subjected to high-pressure homogenization, while the emulsion made by ultrasonic emulsification remained stable during 30 days storage. Ultrasonic emulsification excels other emulsifying techniques such as high-pressure homogenization, high-shear mixing and microfluidization by efficiency, consistent production of nano-droplets, high-emulsion stability and capability to treat any volume from small tubes and beakers to large streams.įor instance, Li and Xiang (2019) showed in their comparative study of high-pressure homogenization and ultrasonic emulsification that ultrasonication yields in more uniform, stable emulsions. This ultrasonic emulsion consists in peppermint essential oil emulsified in a continuous water phase. The curve shoes the nano-scale droplet distribution of an ultrasonically dispersed oil-in-water nanoemulsion. The very small droplet size and the homogeneous, even droplet size distribution of ultrasonically prepared emulsions turns sonication into the preferred emulsification technique. Ultrasonic emulsification can easily generate nano-sized particles with droplet sizes of down to 10nm. These highly intense forces disrupt the two immiscible liquid phases into minute droplets and mixes them uniformly with each other. Ultrasonic emulsifiers use acoustic cavitation, which is characterized by intense high-shear forces and turbulences in the liquid. If oil (dispersed phase) is dispersed in water (continuous phase), it is an oil-in-water emulsion if water droplets are added into an oily continuous phase, it is called a water-in-oil emulsion.įor oil-in-water emulsions, the resulting emulsion quality depends on the formulation (oil:water ratio, emulsifying agent) and the emulsification technique. Small droplets of oil are finely dispersed in the water phase (continuous phase) to create this oil-in-water emulsion. Definition of Oil-in-Water EmulsionĪn oil-in-water emulsion is a mixture in which an oily phase is dispersed in water or another aqueous liquid. material science, polymers, paints, coatings, fine chemistry etc.). Oil-in-water (O/W) emulsions are widely used in many consumer products such as food, beverages, cosmetics, pharmaceuticals etc. Ultrasonic emulsions excel by uniform droplet dispersion and long-term stability therefore being widely used in laboratories and industry. Ultrasonic emulsifiers are well-established to prepare oil-in-water emulsions and nano-emulsions. For oil-in water emulsions, the oily phase (dispersed phase) is evenly mixed into the aqueous phase (continuous phase). An emulsion consists of two immiscible liquids, which are finely dispersed in each other.
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